1. Field of the Invention
This invention relates to a boring bar intended for internal turning, e.g., in a hole in a workpiece. Preferably, the boring bar includes a center axis that extends toward a front part. The front part may include a front end surface and a pocket, which includes a shelf-like surface and a ramp surface. Preferably, the ramp surface extends obliquely/rearward from the shelf surface. A turning insert may be disposed in an insert seat, which is countersunk in the shelf surface and displaced toward one side of the center axis. A chip flute is preferably recessed into an exterior surface of the bar and disposed on the same side of the center axis as the insert seat. Preferably, the chip flute includes a front opening at the ramp surface.
2. Description of Related Art
Internal turning may be carried out in pre-drilled holes, pre-formed holes, etc. in cast, extruded, or otherwise manufactured workpiece blanks, e.g., metal workpiece blanks. Open holes are through going, i.e., open at opposite ends, while closed holes have only one opening and end in a bottom. Internal turning is frequently used in applications with stringent requirements for dimensional tolerances and surface finish. As compared to external turning, there are certain specific difficulties associated with internal turning including a limited boring depth because unacceptably strong vibrations may occur when the boring bar is too long and slender. Accordingly, internal turning is conventionally limited to holes having a depth that is at most 3 to 6 times the diameter of conventional boring bars. Another difficulty is chip evacuation. Insofar as it is generally desirable to provide a hole with a good surface finish, it is preferably that the chips formed by internal turning should not be allowed to aggressively contact the finished hole surface inasmuch as the chips commonly have sharp edges that may mar the finish. In other words, it is preferable to quickly and efficiently evacuate the chips from the hole. Conventionally, this may be achieved as long as the hole is open and/or has a diameter that is sufficiently great to receive a conventional boring bar that has a considerably smaller diameter. That is to say, conventional boring bars need ample space between the envelope surface of the bar and the hole surface so as to allow chips to pass fairly freely. However, the problem of chip evacuation is accentuated when it is desired to turn small, closed holes, i.e., holes having bottoms and diameters of 12 millimeters (mm) or less, e.g., 6 mm or less. However, in order to provided a boring bar that is stable, i.e., that is as vibration free as possible, and that has the ability to carry a replaceable turning insert, conventional boring bars are made with a diameter that is just slightly less than the diameter of the hole. Consequently, the annular space available between the envelope surface of a conventional boring bar and the hole surface is reduced to a minimum size (frequently 1 mm or less). In order to even be able to evacuate the chips from a closed hole under such circumstances, a related boring bar is provided with an external chip flute, e.g., a groove that is countersunk in the envelope surface of the related boring bar and that extends a distance rearward from a forward pocket in which the turning insert is mounted. However, a shortcoming of this related boring bar is that the chips may move in an uncontrolled way in the forward pocket, i.e., without any guidance toward the chip flute.
Conventional turning tools for external turning are per se usually made with internal channels for feeding cooling liquid to the turning insert. However, the mouth of the cooling-liquid channel is conventionally disposed to feed the cooling liquid forward from behind the turning insert, i.e., not a rearward direction toward a chip flute opening.